Technical Field
The present invention relates to a steering wheel having a heating element and a fail-safety device using the steering wheel, in which even when an open circuit occurs in a portion of a heating element coated on the entire surface of a rim for warm holding in winter, the heat emission performance of the rim does not degrade, and if a resistance of the heating element increases over a predetermined value due to damage of the heating element, over-heating is prevented.
Related Art
A rim of a steering wheel, which is an element of a steering wheel, is held at all times and manipulated by a driver, and has been researched and developed in various aspects such as elegance of an exterior, convenience in holding, and adoption of functional elements.
In particular, at an initial stage of driving in winter, the temperature of the rim of the steering wheel is lower than that of the human body, inconveniencing the driver when holding the rim and accordingly, making driving unsafe.
In line with this, various devices have been developed to heat the rim of the steering wheel over a higher temperature than that of the human body.
As examples of techniques for heating the rim of the steering wheel, Korean Utility Model Application No. 1989-0020599, Korean Patent Application No. 1992-0000945, and Korean Utility Model Application No. 1996-0016958 disclose a steering wheel rim structure (see FIG. 1) in which a heating line 3 is buried in a rim 5 of a steering wheel.
As a way to lay the heating line 3, as illustrated in FIG. 2, an insulating coating material 2 is coated onto an outer side of a core 1, and the heating line 3 is adhered to an outer circumferential surface of the insulating coating material 2 and finished with a finishing member 4 such as a synthetic resin material.
However, as illustrated in FIG. 3, for a steering wheel 100 using a sophisticated decorating element such as leather 101, it is difficult to adopt a heating line as a heating element.
As illustrated in FIG. 4, for a sophisticated steering wheel, a certain section of the steering wheel is formed of foaming urethane 102 (a first molding) and is finished by being wrapped by natural leather 101 (wrapping of natural leather 101), and the other section is softened with ABS or soft urethane 103 (a second molding) and is applied various patterns 106 such as a tree pattern, a hair line, a marble pattern, and the like through liquid pressure transfer.
As illustrated in FIG. 5, instead of burying a heating line in a rim, conductive paint, which is a heating element, is coated onto a surface of a steering wheel by using a spraying method, and then is dried to make a heating element. In this case, however, some problems occur in a treated groove 105 due to a spray coating layer 120.
That is, the coating layer 120 becomes thick (as indicated by A) due to the congestion of the conductive paint, caused by a surface tensile force at an edge portion of the treated groove 105, or the conductive paint becomes thin (as indicated by B) at an edge portion due to static electricity, disturbing the flow of electricity in the treated groove 105 and peeling the conductive paint during post-processing such as enclosing with leather, or the like.
When the coating layer 120 is formed in the treated groove 105 by using a spraying method, a bubble phenomenon occurs due to spraying, increasing an electrical conduction defective rate and making the thickness of coating layer be non-uniform.
Besides, the whole or partial an open circuit of a heating line circuit may occur in various portions for various reasons. Moreover, as partial damage occurs in a portion of a heating element, over-current flows in other portions where the damage does not occur, causing a local temperature increase that leads to fire.